In fully optical communication networks, particularly metropolitan ring communication networks, which are in the process of being set up or upgraded, optical fibers between two neighboring network nodes, which fibers are available for the connection of neighboring network nodes to one another, are frequently not fully occupied. In other words, a multiple access of the individual optical fibers using the wavelength division multiplex technique known as WDM is not necessary in such an upgrading stage or when the present fiber capacities of the optical communication network are utilized at such a low level.
In conventionally known network architectures, it is possible to provide an unused optical fiber that connects several network nodes to one another for one network customer exclusively, over which fiber the network customer can receive data from the fiber-optic communication network or transmit data to it. These kinds of optical fibers which are reserved for one network customer are known in the field as xe2x80x9cdark fibersxe2x80x9d, due to the fact that the optical signal transmitted in the optical fiber in the fiber-optic communication network is generally by the laser of the network customer, exclusively, and the optical signal received in the network node is never converted and resent, for example with another wavelength, by the network operator.
In these types of network architectures, however, the possibility of providing a dark fiber is only provided in addition to the primary data transmission with the aid of the WDM technique. Thus, usually the optical feed fibers of a network customer are led to the WDM multiplexer situated in the network node, with the aid of which the optical signals received in the network nodes via several feed fibers are multiplexed into a common optical fiber connecting the individual network nodes (see xe2x80x9cA Cost Effective Approach to Introduce an Optical WDM Network in the Metropolitan Environmentxe2x80x9d, Johansson et al, IEEE Journal on Selected Areas in Communications, Vol. 16, No. 7, September 1998, pp. 1109-1121). However, when a network customer is connected via such dark fibers, it is not possible to monitor the transmission quality or to detect the transmitted data rates, which may be necessary for a charge increase on the part of the network operator. In addition, safety measures have not been provided in known communication networks in case of operational failure of the dark fibers, such as the emission of an alarm signal to the respective optical network node, by which measures it would have been possible to localize errors quickly and reliably. In addition, until now, there has been no known protective circuits for the dark fibers which could effectuate a changeover onto the redundant optical dark fiber in case of breakage of the active optical dark fiber. Because of the absence of these surface capabilities, it is possible for the network operator to provide only extremely few network customers with a connection via a dark fiber.
In addition, from the network operator""s perspective for the sake of optimal exploitation of the usually available fiber capacities (for instance, up to 100 optical ring fibers) and particularly for the sake of upgrading an existing fully optical communication network, it is desirable to be able to operate the fully optical communication network without the aid of the WDM technique and to make possible a gradual implementation of the WDM technique in the course of the network upgrade; in other words, to be able to set up the fiber-bound communication network in a modular fashion.
The object of the present invention is to improve the connection of the network customers to the optical fibers connecting the network nodes of the fiber-optic communication network, with respect to the monitoring of the optical fibers or the optical feed fibers, the regeneration of the optical signals, and the reliability of the connections that are connected via the optical fibers or, respectively, the optical feed fibers. Thus, it is possible to make a gradual upgrading of the optical communication network, initially without using the WDM technique.
The object is achieved in accordance with the improvement in a transparent fiber-optic communication network having several central systems that are connected to one another via optical fibers, to which systems at least one decentralized system is connected via two optical fibers. The improvement is that at least one of the central systems has monitoring equipment and a first optical fiber is connected to one of the decentralized optical systems by a first optical feed fiber in an optically transparent fashion through the monitoring equipment and a second optical fiber is connected to this one decentralized optical system by a second optical feed fiber in an optically transparent manner through the monitoring equipment.
The essential aspect of the inventive transparent fiber-optic communication network having several central systems that are connected to one another via optical fibers, to which at least one decentralized system is respectively connected via two optical feed fibers is that a first optical fiber is connected by a first optical feed fiber to one of the decentralized optical systems in an optically transparent manner via a monitoring equipment and that a second optical fiber is connected by a second optical feed fiber to this decentralized optical equipment in an optically transparent manner via the monitoring equipment. In the inventive transparent fiber-optic communication network, the feed fibers of a decentralized system, for example the communication equipment of the network customer, are advantageously led to the as yet unused optical fibers connecting the central optical system. It thus becomes possible to forego the cost-intensive and, in the set-up of a communication network partially inefficient, provision of a WDM multiplexer in the central system, especially since multiple usage of the individual optical fibers with the aid of the WDM technique represents a high technical cost, which is unnecessary due to the typically low load on the communication network during set-up or, respectively, the upgrading of the communication network. In addition, the inventive monitoring equipment advantageously ensures a reliable and safe operation, both of the optical feed fibers and of the optical ring fibers and thereby makes possible a rapid and reliable localization of errors given a failure of the optical fibers or the optical feed fibers. In addition, by virtue of the module construction of the inventive communication network, it is possible to expand the communication network or, respectively, the respective optical network node, by a WDM multiplexer for multiple accessing of individual optical fibers, which is necessary given increasing usage of the communication network.
According to a further development of the inventive method, the fiber optical fiber is connected by the first optical feed fiber to the decentralized optical system in an optically transparent manner via a regeneration equipment or unit as well as the monitoring equipment, and the second optical fiber is connected to the decentralized system by the regeneration equipment or unit as well as the monitoring equipment in an optically transparent manner by the second feed fiber. The regeneration equipment or unit is provided for the purpose of restoring the optical transmitted level of the optical signals that are transmitted over the optical feed fiber and/or over the optical fibers. Due to the regeneration equipment, the optical signals that are received in the network nodes are not only monitored by the monitoring equipment, but also regenerated so that the original optical signals is partly or completely recovered, for instance with respect to its transmitted level, and can thus be transmitted more reliably. The number of transmission errors generated by an optical signal level that is too weak is thus reduced.
An advantageous development is that the monitoring equipment is provided for monitoring the data rate of the data currently being transmitted between the decentralized and the central optical systems. Advantageously, the data rate used by the network customer for transmission of his data into and out of the fiber-optic communication network can be monitored by the inventive monitoring equipment, and thus the costs that accrue for the use of the fiber-optic communication network can be indicated to the network customer by the network operator in a transparent manner.
Other advantages and features of the invention will be readily apparent from the following description of the preferred embodiments, the drawings and claims.